A test spectral sensitivity curve was measured on 3-month-old human infants using a steady 8 degrees test light on a 580 nm adapting field. The data show a "Sloan" notch near 580 nm and a peak near 610 nm. The results are compared to standard nonopponent and opponent models of color vision, and it is concluded that 3-month-old infants have a chromatically opponent detection channel.